1. Field of the Invention
The present invention relates to a lock nut to be employed for fastening articles by tightening it on a bolt and is intended to hold the applied tightening force for a long time by devising the inside of the nut.
2. Description of the Related Art
In the prior art, the means for preventing the nut from becoming loose has been disclosed in Examined Published Japanese Patent Application No. 3-526, for example. Here a lower nut is used, in which a convex taper block is formed on the upper face thereof with an eccentricity relative to the axis of a thread, and an upper nut in which a recess concentric to the axis of the thread is formed to be fitted on the convex portion of the taper block. The nut is locked by a wedge effect at the taper portion by first tightening the lower nut on the bolt in an ordinary manner and then by tightening the upper nut.
This nut requires tightening twice because of the double type. When the tightening requires a torque wrench, the upper and lower nuts are simultaneously tightened so that the locking effect cannot be expected as a matter of fact. On the other hand, when the nut is to be removed, the thread portion may be broken when the loosening operation starts from the lower nut.